Investment Securities - Consolidated Venture Capital and Private Equity Fund Investments (Details) - Consolidated venture capital and private equity fund investments - Fair value accounting - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Nonmarketable securities	$ 88,937	$ 87,180
Strategic Investors Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 4,850	$ 5,729
Strategic Investors Fund, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	12.60%	12.60%
Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 49,574	$ 45,341
Capital Preferred Return Fund, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	20.00%	20.00%
Growth Partners, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 34,513	$ 35,976
Growth Partners, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	33.00%	33.00%
CP I, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 0	$ 134
CP I, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	0.00%	10.70%